1. Field of the Invention
The present invention relates to processes and equipment for the continuous or batchwise treatment of wastewater containing hydrocarbon contaminants.
2. Description of the Prior Art
Petroleum bulk storage facilities for such products as gasoline and diesel fuel generate quantities of wastewater which are contaminated with hydrocarbon components or contaminants. Floating top petroleum storage tanks accumulate some quantity of water due to seepage around wall seals. Wastewater may also be generated from contaminated bulk shipments which are loaded into the tanks. Once inside a petroleum bulk storage tank, water settles to a sump area which is periodically pumped out to remove the water contamination. Furthermore, petroleum bulk storage facilities have rail or truck transfer stations at which small quantities of petroleum products are spilled during hook-up and disconnect of bulk transfer equipment. The petroleum products associated with these small spills are collected in spill-containment sumps where they mix with storm water. Contaminated wastewater may also include groundwater which has been contaminated by a migrating plume of hydrocarbon contaminants from a spill or tank leak. Prior to recently promulgated Environmental Protection Agency regulations, such hydrocarbon-contaminated wastewater was typically dumped on the ground or hauled as non-hazardous waste to disposal facilities.
The wastewater that is generated from the above sources often contains elevated levels of benzene along with varying concentrations of toluene, ethylbenzene and xylenes. Other petroleum hydrocarbons will also be present. On Mar. 29, 1990, the Environmental Protection Agency (EPA) promulgated the revised toxicity characteristics rule. Benzene, a water-soluble hydrocarbon compound which is present in gasoline, was included in the list of newly-included constituents. Under the new regulation, a benzene concentration of 0.5 mg/l would trigger classification of the wastewater as a hazardous waste and subject such stream to stringent EPA hazardous waste management standards. The wastewater generated must therefore be treated to remove chemicals which the EPA would classify as triggering a hazardous waste designation, in particular benzene, but also other hydrocarbon contaminants which face discharge restrictions by state environmental agencies.
In order to meet environmental regulations, generators of hydrocarbon-contaminated wastewater such as petroleum bulk storage facilities, both large and small, must install or have available to them, methods for treatment of such wastewater. This requires a system which is economically feasible for generators of varying size while minimizing operating labor requirements.
A need exists for a continuous or batchwise system which removes benzene and other hydrocarbon contaminants from wastewater generated at petroleum bulk storage facilities. Preferably the process or system is one which reduces the concentration of such contaminants to below EPA and state environmental agency acceptable maximum levels. Furthermore, there is a need for a system which combines the necessary equipment to remove hydrocarbon contaminants in a complete system which is economical and requires minimum operating labor. The present invention addresses these needs as well as other problems associated with cleaning wastewater generated at petroleum bulk storage facilities in an advantageous manner.